Whare is it located? Is there a file, or is it in the database?
It's in the database, in a table called themes. You can access them in the Admin CP by going to the Themes section.
Thanks that is what I thought.
The themes manager is exactly in Admin CP > Themes > Modify / Delete > Edit theme
You can have multiple themes at the same time also.
Yes, I knew that already thank you, I had lost an old theme and I had a bakup of the files, I am trying to restore the files now